These are easy to build and I have it monitoring my fridgerator circuit - one with 3 fridges on it.
Another option is @iharyadi's environmental sensor. I purchased several of these because I also wanted humidity, temp, etc too and it is capable to alert you of a power outage since it has a backup battery option. As you may have seen in the post @aaiyar mentioned above I originally built the power sensor for my sump pump but I have since switched it out for Iman's sensor so I can monitor humidity in the crawl space too.